Network Working Group F. Templin, Ed. Internet-Draft Boeing Research & Technology Intended status: Informational September 22, 2017 Expires: March 26, 2018 IPv6 Prefix Delegation for End Systems draft-templin-v6ops-pdhost-10.txt Abstract IPv6 prefixes are typically delegated to requesting routers which then use them to number their downstream-attached links and networks. This document considers the case when the requesting router is an end system which receives a delegated prefix that it can use for its own sub-delegation and/or multi-addressing purposes. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. 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Templin Expires March 26, 2018 [Page 1] Internet-Draft Prefix Delegation for End Systems September 2017 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Multi-Addressing Considerations . . . . . . . . . . . . . . . 6 4. Multi-Addressing Alternatives for Delegated Prefixes . . . . 6 5. MLD/DAD Implications . . . . . . . . . . . . . . . . . . . . 7 6. Dynamic Routing Protocol Implications . . . . . . . . . . . . 7 7. IPv6 Neighbor Discovery Implications . . . . . . . . . . . . 8 8. ICMPv6 Implications . . . . . . . . . . . . . . . . . . . . . 8 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 10. Security Considerations . . . . . . . . . . . . . . . . . . . 9 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 12.1. Normative References . . . . . . . . . . . . . . . . . . 9 12.2. Informative References . . . . . . . . . . . . . . . . . 10 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11 1. Introduction IPv6 Prefix Delegation (PD) entails 1) the communication of a prefix from a delegating router to a requesting router, 2) a representation of the prefix in the delegating router's routing table, and 3) a control messaging service between the delegating and requesting routers to maintain prefix lifetimes. Following delegation, the prefix is available for the requesting router's exclusive use and is not shared with any other nodes. An example IPv6 PD service is the Dynamic Host Configuration Protocol for IPv6 (DHCPv6) [RFC3315][RFC3633]. This document considers the case when the requesting router is actually an end system (ES) that can act as a router on behalf of its downstream networks and as a host on behalf of its local applications. The following paragraphs present possibilities for ES behavior upon receipt of a delegated prefix. For ESes that connect downstream-attached (aka "tethered") networks, a Delegating Router 'D' delegates a prefix 'P' to a Requesting ES 'R' as shown in Figure 1: Templin Expires March 26, 2018 [Page 2] Internet-Draft Prefix Delegation for End Systems September 2017 +---------------------+ |Delegating Router 'D'| | (Delegate 'P') | +----------+----------+ | | Upstream link | +----------+----------+ | Upstream Interface | +---------------------+ | | | Requesting ES 'R' | | (Receive 'P') | | | +---------------------+ | Downstream Interface| +--+-+--+-+--+-----+--+ |A1| |A2| |A3| ... |An| +--+-+--+-++-+-----+--+ | | Downstream link | X----+-------------+--------+----+---------------+---X | | | | +---++-+--+ +---++-+--+ +---++-+--+ +---++-+--+ | |X1| | | |X2| | | |X3| | | |Xn| | | +--+ | | +--+ | | +--+ | | +--+ | | Host H1 | | Host H2 | | Host H3 | ... | Host Hn | +---------+ +---------+ +---------+ +---------+ <-------------- Tethered Network -------------> Figure 1: Classic Routing End System Model In this figure, when Delegating Router 'D' delegates prefix 'P', it inserts 'P' into its routing table with Requesting ES 'R' as the next hop. Meanwhile, 'R' receives 'P' via an upstream interface and sub- delegates 'P' to its downstream external (physical) and/or internal (virtual) networks. R assigns addresses 'A(i)' taken from 'P' to downstream interfaces, and Hosts 'H(i)' on downstream networks assign addresses 'X(i)' taken from 'P' to their interface connections to the downstream link. 'R' then acts as a router between hosts 'H(i)' on downstream links and correspondents reachable via other interfaces. This document also considers the case when 'R' does not have any physical downstream interfaces, and can use 'P' solely for its own internal addressing purposes. In that case, 'R' assigns 'P' to a Templin Expires March 26, 2018 [Page 3] Internet-Draft Prefix Delegation for End Systems September 2017 virtual interface (e.g., a loopback), and acts as a router that forwards packets between the upstream and virtual interfaces. 'R' can then function under the weak end system model [RFC1122][RFC8028] by assigning addresses taken from 'P' to a virtual interface as shown in Figure 2: +---------------------+ |Delegating Router 'D'| | (Delegate 'P') | +----------+----------+ | | Upstream link | +----------+----------+ | Upstream Interface | +---------------------+ | | | Requesting ES 'R' | | (Receive 'P') | | | +---------------------+ | Virtual Interface | +--+-+--+-+--+-----+--+ |A1| |A2| |A3| ... |An| +--+-+--+-+--+-----+--+ Figure 2: Weak End System Model 'R' could instead function under the strong end system model [RFC1122][RFC8028] by assigning IPv6 addresses taken from 'P' to an upstream interface as shown in Figure 3: Templin Expires March 26, 2018 [Page 4] Internet-Draft Prefix Delegation for End Systems September 2017 +---------------------+ |Delegating Router 'D'| | (Delegate 'P') | +----------+----------+ | | Upstream link | +----------+----------+ | Upstream Interface | +--+-+--+-+--+-----+--+ |A1| |A2| |A3| ... |An| +--+-+--+-+--+-----+--+ | | | Requesting ES 'R' | | (Receive 'P') | | | +---------------------+ | Virtual Interface | +---------------------+ Figure 3: Strong End System Model The major benefit for an ES managing a delegated prefix in either the weak or strong end system models is multi-addressing. With multi- addressing, the ES can configure an unlimited supply of addresses to make them available for local applications without requiring coordination with any other nodes on upstream interfaces. The following sections present considerations for ESes that employ prefix delegation mechanisms. 2. Terminology The terminology of the normative references apply. The following terms are defined for the purposes of this document: node, host, router the same as defined in [RFC8200]. End System (ES) a node that acts as a host on behalf of its local applications and as a router on behalf of its downstream interface(s), but does not forward packets received on an upstream interface via the same or a different upstream interface (see: Security Considerations). shared prefix Templin Expires March 26, 2018 [Page 5] Internet-Draft Prefix Delegation for End Systems September 2017 an IPv6 prefix that may be advertised to more than one node on the link, e.g., in a Router Advertisement (RA) message Prefix Information Option (PIO) [RFC4861]. individual prefix an IPv6 prefix that is advertised to exactly one node on the link (e.g., in an RA PIO), where the node is a passive recipient of the prefix. delegated prefix an IPv6 prefix that is conveyed to an ES for its own exclusive use, where the ES is an active participant in the prefix delegation and maintenance procedures. 3. Multi-Addressing Considerations IPv6 allows nodes to assign multiple addresses to a single interface. [RFC7934] discusses options for multi-addressing as well as use cases where multi-addressing may be desirable. Address configuration options for multi-addressing include StateLess Address AutoConfiguration (SLAAC) [RFC4862], stateful DHCPv6 address configuration [RFC3315], manual configuration, etc. ESes configure addresses from a shared or individual prefix and assign them to the upstream interface over which the prefix was received. When it assigns the addresses, the ES is required to use Multicast Listener Discovery (MLD) [RFC3810] to join the appropriate solicited-node multicast group(s) and to use the Duplicate Address Detection (DAD) algorithm [RFC4862] to ensure that no other node configures a duplicate address. In contrast, an ES that uses address configuration from a delegated prefix can assign addresses without invoking MLD/DAD on an upstream interface, since the prefix has been delegated to the ES for its own exclusive use and is not shared with any other nodes. 4. Multi-Addressing Alternatives for Delegated Prefixes When an ES receives a prefix delegation, it has many alternatives for provisioning the prefix. [RFC7278] discusses alternatives for provisioning a prefix obtained by a User Equipment (UE) device under the 3rd Generation Partnership Program (3GPP) service model. This document considers the more general case when the ES receives a prefix delegation in which the prefix is explicitly delegated for its own exclusive use. When the ES receives the prefix, it can distribute the prefix to downstream interfaces and configure one or more addresses for itself Templin Expires March 26, 2018 [Page 6] Internet-Draft Prefix Delegation for End Systems September 2017 on downstream interfaces. The ES then acts as a router on behalf of its downstream-attached networks and configures a default route via a neighbor on an upstream interface. The ES could instead (or in addition) use portions of the delegated prefix for its own multi-addressing purposes. In a first alternative, the ES can assign the prefix to a virtual interface and assign one or more addresses taken from the prefix to virtual interfaces. In that case, ES applications can use the assigned addresses according to the weak end system model. In a second alternative, the ES can assign the prefix to a virtual interface and assign one or more addresses taken from the prefix to the upstream interface over which the prefix was received. In that case, ES applications can use the assigned addresses according to the strong end system model. In both of these latter two cases, the ES acts as a host on behalf of its local applications and as a router from the standpoint of packet forwarding, prefix delegation and neighbor discovery over upstream interfaces. The ES can configure as many addresses for itself as it wants. 5. MLD/DAD Implications When an ES configures addresses for itself from a shared or individual prefix, the ES performs MLD/DAD by sending multicast messages over upstream interfaces to test whether there is another node on the link that configures a duplicate address. When there are many such addresses and/or many such nodes, this could result in substantial multicast traffic that affects all nodes on the link. When an ES configures addresses for itself from a delegated prefix, the ES can configure as many addresses as it wants but does not perform MLD/DAD for any of the addresses over upstream interfaces. This means that the ES can configure arbitrarily many addresses without causing any multicast messaging over the upstream interface that could disturb other nodes. 6. Dynamic Routing Protocol Implications The ES can be configured to either participate or not participate in a dynamic routing protocol over the upstream interface, according to the deployment model. When there are many ESes on the upstream link, dynamic routing protocol participation might be impractical due to scaling limitations, and may also be exacerbated by factors such as ES mobility. Templin Expires March 26, 2018 [Page 7] Internet-Draft Prefix Delegation for End Systems September 2017 Unless it participates in a dynamic routing protocol, the ES initially has only a default route pointing to a neighbor via an upstream interface. This means that packets sent by the ES over an upstream interface will initially go through a default router even if there is a better first-hop node on the link. 7. IPv6 Neighbor Discovery Implications The ES acts as a simple host to send Router Solicitation (RS) messages over upstream interfaces (i.e., the same as described in Section 4.2 of [RFC7084]) but also sets the "Router" flag to TRUE in any Neighbor Advertisement messages it sends. The ES does not send RA messages over upstream interfaces. The current first-hop router may send a Redirect message that updates the ES's neighbor cache so that future packets can use a better first-hop node on the link. The Redirect can apply either to a singleton destination address, or to an entire destination prefix as described in [I-D.templin-6man-rio-redirect]. 8. ICMPv6 Implications The Internet Control Message Protocol for IPv6 (ICMPv6) includes a set of control message types [RFC4443] including Destination Unreachable (DU). According to [RFC4443], routers SHOULD return DU messages (subject to rate limiting) with code 0 ("No route to destination") when a packet arrives for which there is no matching entry in the routing table, and with code 3 ("Address unreachable") when the IPv6 destination address cannot be resolved. According to [RFC4443], hosts SHOULD return DU messages (subject to rate limiting) with code 3 to internal applications when the IPv6 destination address cannot be resolved, and with code 4 ("Port unreachable") if the IPv6 destination address is one of its own addresses but the transport protocol has no listener. An ES that obtains and manages a prefix delegation per this document observes the same procedures as described for both routers and hosts above. 9. IANA Considerations This document introduces no IANA considerations. Templin Expires March 26, 2018 [Page 8] Internet-Draft Prefix Delegation for End Systems September 2017 10. Security Considerations Security considerations for IPv6 Neighbor Discovery [RFC4861] and any applicable prefix delegation mechanisms apply to this document. Additionally, the ES may receive unwanted IPv6 packets via an upstream interface that match a delegated prefix but do not match a configured IPv6 address. In that case, the ES drops the packets and observes the "Destination Unreachable - Address unreachable" procedures in Section 8. The ES may also receive IPv6 packets via an upstream interface that do not match any of the ES's delegated prefixes. In that case, the ES drops the packets and observes the "Destination Unreachable - No route to destination" procedures in Section 8. This is necessary to avoid reflection attacks that would cause the ES to forward packets received from an upstream interface via the same or a different upstream interface. 11. Acknowledgements This work was motivated by recent discussions on the v6ops list. Mark Smith pointed out the need to consider MLD as well as DAD for the assignment of addresses to interfaces. Ricardo Pelaez-Negro, Edwin Cordeiro, Fred Baker, Naveen Lakshman, Ole Troan, Bob Hinden, Brian Carpenter, Joel Halpern and Albert Manfredi provided useful comments that have greatly improved the document. 12. References 12.1. Normative References [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, DOI 10.17487/RFC0791, September 1981, . [RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, C., and M. Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July 2003, . [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic Host Configuration Protocol (DHCP) version 6", RFC 3633, DOI 10.17487/RFC3633, December 2003, . Templin Expires March 26, 2018 [Page 9] Internet-Draft Prefix Delegation for End Systems September 2017 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener Discovery Version 2 (MLDv2) for IPv6", RFC 3810, DOI 10.17487/RFC3810, June 2004, . [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification", STD 89, RFC 4443, DOI 10.17487/RFC4443, March 2006, . [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, DOI 10.17487/RFC4861, September 2007, . [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless Address Autoconfiguration", RFC 4862, DOI 10.17487/RFC4862, September 2007, . [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", STD 86, RFC 8200, DOI 10.17487/RFC8200, July 2017, . 12.2. Informative References [I-D.templin-6man-rio-redirect] Templin, F. and j. woodyatt, "Route Information Options in IPv6 Neighbor Discovery", draft-templin-6man-rio- redirect-04 (work in progress), August 2017. [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - Communication Layers", STD 3, RFC 1122, DOI 10.17487/RFC1122, October 1989, . [RFC7084] Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic Requirements for IPv6 Customer Edge Routers", RFC 7084, DOI 10.17487/RFC7084, November 2013, . [RFC7278] Byrne, C., Drown, D., and A. Vizdal, "Extending an IPv6 /64 Prefix from a Third Generation Partnership Project (3GPP) Mobile Interface to a LAN Link", RFC 7278, DOI 10.17487/RFC7278, June 2014, . Templin Expires March 26, 2018 [Page 10] Internet-Draft Prefix Delegation for End Systems September 2017 [RFC7934] Colitti, L., Cerf, V., Cheshire, S., and D. Schinazi, "Host Address Availability Recommendations", BCP 204, RFC 7934, DOI 10.17487/RFC7934, July 2016, . [RFC8028] Baker, F. and B. Carpenter, "First-Hop Router Selection by Hosts in a Multi-Prefix Network", RFC 8028, DOI 10.17487/RFC8028, November 2016, . Author's Address Fred L. Templin (editor) Boeing Research & Technology P.O. Box 3707 Seattle, WA 98124 USA Email: fltemplin@acm.org Templin Expires March 26, 2018 [Page 11]